The long-term goals of this research are to define the neural projections from individual vestibular receptors in the pigeon labyrinth with modern neuroanatomic tract-tracing techniques, and to identify each receptor's contribution to the organization of primary and secondary vestibular pathways in the brain and spinal cord. Our specific objectives are (1) to investigate the pattern of receptor-receptor interconnections and afferent convergence across receptor types in Scarpa's ganglion in double-label studies with fluorescent neural tracers and horseradish peroxidase, (2) to investigate the pattern of vestibular efferent divergence across receptor types in the pigeon labyrinth in similar double-label studies, and (3) to delineate the telencephalic projections from the pigeon labyrinth by transneuronal transport of 3H-proline-fucose injected and contained within the endolymphatic space of the membranous labyrinth. We expect these studies to provide a clearer understanding of the neuroanatomic relationship between afferent and efferent vestibular projections, and give data of significance to electrophysiologists. The results may also be of importance for better understanding the mechanisms underlying certain common clinical vestibular disorders.